Electrolytic grinding machine

ABSTRACT

An electrolytic grinding machine having a grinding wheel comprises an electrolytic grinding device, means for detecting the electrolytic grinding current and a control system for controlling the speed at which the grinding wheel head is advanced toward a workpiece. The workpiece is ordinarily by the electrolytic grinding device. However, when the electrolytic grinding current becomes smaller than a perdetermined current such that the grinding efficiency decreases, a conventional grinding operation by the grinding wheel is automatically applied on the workpiece in response to a command signal provided by the control system.

Sept. 26, 1972 KUNIO TAKAHASHI I ELECTROLYTIC GRINDING MACHINE 3 Sheets-Sheet 1 Filed NOV. 17, 1970 INVENTOR KUNIO TAKAHASHI BY 061M, PM W ATTORNEYS p 1972 KUNIO TAKAHASHI 3,69

ELECTROLYTIC GRINDING MACHINE Filed Nov. 17; 1970 s Sheets-Sheet z WHEEL INFEED AMOUNT OF THE GRINDING REMOVAL AMOUNT OF THE WORKPIECE Sept. 26, 1972 KUNIO TAKAHASHI ELECTROLYTIC GRINDING MACHINE 3 Sheets-Sheet 5 Filed Nov. 17, 1970 United States Patent 3,694,340 ELECTROLYTIC GRINDING MACHINE Kunio Takahashi, Nagoya, Japan, assignor to Toyoda Koki Kabushiki Kaisha, Kariya-shi, Aichi-ken, Japan Filed Nov. 17, 1970, Ser. No. 90,280 Claims priority, application Japan, Dec. 8, 1969, 44/98 535 Int. Cl. B23 1/00 US. Cl. 204-224 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates generally to electrolytic grinding and more particularly to an improved electrolytic grinding machine wherein a cylindrical workpiece is ground by means of an electrolytic grinding operation and a conventional grinding operation arranged to be automatically performed in a cooperative and efiicient manner.

Heretofore, in conventional electrolytic grinding machines having a workpiece and a conductive grinding wheel, the conductive grinding wheel has been maintained in predetermined spaced relation relative to the workpiece by abrasive particles which are bonded on the surface of the grinding wheel, and a direct-current has been applied between the conductive grinding wheel and the workpiece while an electrolyte is simultaneously supplied therebetween. Consequently, while the workpiece and the grinding wheel head of these previous devices are being rotated in a conventional manner, the grinding wheel head is advanced toward the workpiece at an appropriate preselected speed, whereby the electrolytic grinding process is started. When the workpiece has been ground to a predetermined size, the direct-current supplied between the workpiece and the conductive grinding wheel is shut off, and afterward the workpiece is conventionally fine finished by the grinding wheel only.

However, since both the workpiece and the grinding wheel are generally constructed in cylindrical c0nfigura tions, the opposing area therebetween, namely the actual area available for electrolytic grinding, is extremely small, so that a large amount of direct-current cannot be applied between the workpiece and the grinding wheel, and the electrolytic grinding efficiency suffers because of it.

Furthermore, as the feeding speed of the grinding wheel head and the electrolytic grinding speed are not suitably controlled, if the feeding speed of the grinding wheel head becomes greater than the electrolytic grinding speed, or in other words, if the grinding wheel is advanced toward the workpiece at a greater speed than that at which the electrolytic grinding process is being performed, then the workpiece will be ground by the grinding wheel rather than by electrolytic grinding. In this case, it is highly likely that the grinding wheel and/or the abrasive particles bonded thereon will suffer extensive wear and damage. Therefore, the beneficial aspects of the combination of electrolytic grinding and conventional wheel grinding 'ice are not fully realized by the electrolytic grinding machines presently available.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide an improved electrolytic grinding machine which avoids the aforementioned disadvantages of previously known electrolytic grinding machines.

Yet another object of the present invention is to provide an electrode shoe adapted to be disposed against the workpiece on the opposite side of the grinding wheel and which is formed to match the contour of the workpiece with a predetermined space being maintained therebetween, whereby an electrolytic grinding area of increased proportions and a corresponding relatively large amount of electrolytic current may be provided between the workpiece and the electrode shoe.

A still further object of the present invention is to provide means for detecting electrolytic grinding current and a control system for controlling the feeding speed of the grinding wheel head of an electrolytic grinding machine, whereby whenever the current becomes smaller than a predetermined current, the control system will be effective to initiate grinding of the workpiece by the grinding Wheel.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and various other objects of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of a preferred embodiment when considered in connection with the accompanying drawings wherein like numerals designate like or corresponding parts throughout the several figures and in which:

FIG. 1 is a sectional view showing a preferred embodiment of the present invention;

FIG. 2 is a perspective view of an electrode shoe forming part of the invention and constructed according to the teachings thereof;

FIG. 3 is a block diagram of a control system applied to the electrolytic grinding machine constructed according to the present invention; and

FIG. 4 is a diagram illustrating an ordinary cycle of a grinding operation performed by the present invention.

DETAILED DESCRIPTION OF THE INVENTION Now, referring to FIG. 1, there is secured on a machine bed 11 of an electrolytic grinding machine a stationary base 12 having a grinding wheel head 13 slidably mounted thereon. A grinding wheel spindle 14 is rotatably journalled in the grinding wheel head 13, and has a conventional grinding wheel 15 positioned at one end thereof and a pulley 16 at the other end. A motor 17 for driving the grinding wheel 15 is mounted on the rear end of the grinding wheel head 13. The pulley 16 on the spindle 14 and another pulley 18 keyed to the drive shaft of the motor 17 are operably connected by a V-belt 19, whereby the motor 17 drives the grinding wheel 15 through the pulleys 16 and 18 and the V-belt 19.

A rapidly feeding hydraulic actuator generally indicated by the numeral 21a is mounted on the rear end of the stationary base 12 and comprises a cylinder 21 and a piston 22 slidably mounted therewithin. The piston 22 is integrally formed on the intermediate portion of an elongate feed shaft 23 having a threaded portion 24 at one end thereof and a splined portion 25 at the other end. The threaded portion 24 is engaged with a threaded block 20 secured to the lower side of the grinding wheel head 13. On the other hand, the splined portion 25 is engaged with the splined portion of a gear 26, which is rotatably mounted in a bracket 27 secured to the rear side of the machine bed 11, with axial movement of the gear 26 being restricted by conventional means. The gear 26 engages another gear 29 which is keyed to the output shaft of an electro-hydraulic pulse motor 28 secured to the rear side of the bracket 27.

When fluid under pressure is supplied to a directional control valve 30 from a fluid pressure source, not shown, and a solenoid of the valve 30 is energized to change the valve 30 to a position indicated at II, fluid under pressure is supplied to the right chamber of the cylinder 21, whereby the grinding wheel head 13 is rapidly advanced toward a workpiece 42 by the piston 22 until the top end of the threaded portion 24 engages a stop plate 31 fixed to the stationary base 12, whereupon the grinding wheel head 13 is then further advanced at a rough grinding feed speed or a fine grinding feed speed by operation of the pulse motor 28 through the threaded block 20, shaft 23 and gear 29.

Reference numerals 32 and 33 designate limit switches fixedly positioned for actuation by a dog plate 34 carried on a shaft 34a extending from the splined end portion 25 of the elongate feed shaft 23. The limit switch 32 confirms the starting position of the grinding wheel head 13 and the switch 33 the final position in the path of movement thereof toward the workpiece negotiated by the piston 22.

On the bed 11, there is also slidably mounted a table 40 on which a head stock 41 and a tail stock, not shown, are mounted for rotatably supporting the workpiece 42. A motor 43 is mounted on the head stock 41 for rotating the workpiece 42 through turning gear mechanism, not shown, provided in the head stock 41.

Between the head stock 41 and the tail stock, the slidable table 40 is provided with a supporting base 44 for supporting the electrolytic grinding device. A movable base 45 is slidably mounted on the supporting base 44 for advancement and retraction relative to the workpiece 42 by a hand wheel 46 mounted on the front side of the supporting base 44. A holding bracket 48 is secured on the movable base 45 through an insulator 47, and has a pivot pin 49 thereon to which support 50 is keyed for thereby pivotably mounting the same on the holding bracket 48. The shaft 49 is usually restricted from the relative pivotable movement in a conventional manner.

A conductive holding member 51 is slidably mounted in the support 50 and restricted from rotational movement therein by any conventional means, such as, for example, by a key relation to the slot within the support, being in the form of a rectangular cross section. A conductive electrode shoe 52 is screwed to the top end of the holding member 51 and disposed opposite the grinding wheel 15, thereby placing the workpiece 42 therebetween. The holding member 51 has a terminal 55 at the rear end thereof, which is connected to the negative pole of a direct current power source 54 through a shunt 53 and a switch 56, and on the other hand, the positive pole of the power source 54 is connected to the slidable table 40 and the workpiece 42 through the head stock 41, the tail stock and other sections of the device. A compression spring 57 is installed between the support 50 and the holding member 51 for biasing the electrode shoe 52 against the workpiece 42.

The electrode shoe 52, as shown in FIG. 2, preferably has an arcuate convex surface 58 thereon, of which the inner radius R is substantially the same radius as that of the workpiece 42, the angle of the circular are between the end edges of the arcuate surface 58 is properly decided by the electrolytic grinding condition, and the transverse length L thereof is approximately equal to the length of the workpiece 42. An axially extending slot 59 providing a delivery port for electrolyte is formed on the intermediate portion of the arcuate convex surface 58, and is connected to an electrolyte supply port 60 disposed on the upper surface of the electrode shoe 52. Therefore, pressurized electrolyte supplied from an electrolyte source 61 may be delivered through the supply port 60 and the delivery port 59 in the electrode shoe 52 onto the workpiece 42. The electrode shoe 52 further has insulating particles 62, such as diamond, uniformly spaced in adhering relation on the whole arcuate surface 58 for spacing the arcuate surface a predetermined distance from the periphery of the workpiece 42 being received in the shoe 52.

A table 63 for slidably supporting a sizing device 64 is fixedly mounted on the slidable table 40 between the head stock 41 and the supporting base 44. The sizing device 64 can he reciprocated relative to the workpiece 42 by means of a piston-cylinder mechanism, not shown, also mounted in the table 63. Moreover, the sizing device 64 is provided with a pair of opposed feelers 65 to engage the workpiece 42 for measuring the diameter thereof. The lower feeler 65 is mechanically interlocked with the core of a differential transformed 86 mounted in the sizing device 64. The output signal from the differential transformer 86 is sent to a main control circuit 70, as shown in FIG. 3, through an amplifier 87 and a pair of Schmitt triggering circuits 88 and 89, presently to be described. Reference numeral 66 designates a coolant supply nozzle for supplying coolant fluid from a coolant fluid source 67 onto the areas of contact between the grinding wheel 15 and the workpiece 42. In this embodiment, the electrolyte serves as the coolant being delivered to the workpiece 42, so the electrolyte and coolant may be supplied from a common fluid source.

Next, referring to FIG. 3, the feed control system for the grinding wheel head 13 will be described. Reference numeral 70 designates the aforementioned main control circuit for controlling the whole mechanical movement of the electrolytic grinding machine by means of signals being sent from various electrical sensing means, such as the limit switches 32 and 33, the sizing device 64, and the like. Reference numeral 71 designates a pulse generator for providing pulse signals in response to the receipt of a signal from the main control circuit 70. Reference numerals 72, 76 and 79 designate AND gates. The AND gate 72 will provide a pulse signal to an input of an OR gate 75 upon the simultaneous receipt of a signal from the pulse generator 71, the comparator 73 and a NOT gate 74. The AND gate 76 will provide a pulse to another input of the OR gate 75 in response to the simultaneous receipt of a signal from the pulse generator 71, after being divided in half by a Flip-Flop gate 78, an inhibit signal from a NOT gate 77 and an inhibit signal from the NOT gate 74. In the above, it should be noted that the inhibit signal at the output of the NOT gate 74 is in response to a fine grinding operation and the output of the NOT gate '77 is in response to an ordinary grinding operation, namely a grinding operation by the grinding wheel 15. The AND gate 79 will provide a pulse to the OR gate 75, after being divided in half by a Flip-Flop 80, in response to the simultaneous receipt of a pulse from the output of the Flip-Flop 78 and a signal representing a fine grinding operation from the main control circuit 70. The reference numeral 81 designates a gate circuit for enabling a forward rotation of the pulse motor 28 and hence an advancement of the grinding wheel head 13 in response to a signal from the OR gate 75. Reference numeral 82 designates a gate circuit for enabling a reverse rotation of the pulse motor 28, and hence a retraction of the grinding wheel head 13 in response to a signal from the main control circuit 70. A reversible counter 83 is provided and the same will add any pulses received from the gate circuit 81 and will subtract any pulses received from the gate circuit 82. When the number in the counter registers a zero count, a signal will be emitted therefrom and applied to the main control circuit 70 for stopping the grinding wheel head 13 and indicating that the same should be returned to its starting position. Reference numeral 84 designates a driving circuit for respectively driving the electro-hydraulic pulse motor 28 in either a forward or reverse direction depending upon whether pulse signals are received from either the gate circuit 81 or the gate circuit 82.

In addition, it should be understood that the aftorementioned shunt 53 is connected between the electrode shoe 52 and the power source 54 for enabling the electrolytic grinding current, which is inversely proportional to electrolytic grinding resistance between the electrode shoe 52 and the workpiece 42, to be detected. It should further be understood that the shunt '53 will provide a voltage control signal to the comparator 73 with an amplitude which is proportional to the electrolytic grinding current in the power source 54. In the comparator 73, when the signal from the shunt 53 exceeds a predetermined reference value, a signal will be applied to the input of the AND gate 72 and the NOT gate 77. The predetermined value of the reference voltage applied to the comparator 73 may be varied in a conventional manner so as to select any desired value. The differential transformer 86 is connected to the pair of Schmitt trigger circuits 88 and 89 through the amplifier 87 and interlocked to the sizing device 64, as hereinbefore indicated. When a signal representative of the diameter of the workpiece 42 is obtained from the differential transformer 86 then a signal for enabling a fine grinding operation is applied from the Schmitt trigger circuit 88 to the main control circuit 70 and a sizing signal is applied from the Schmitt trigger 89 to the main control circuit 70.

Now, hereinbelow explained is the operation of the above described embodiment of the present invention with particular reference to FIGS. 1, 3, and 4. FIG. 4 diagrams the cycle of the grinding operation in which the solid lines show the infeed amount of the grinding wheel head 13 respective to time and the broken lines show the removal amount of the workpiece 42 by means of the electrolytic grinding operation respective to time. When the main control circuit 70 receives a starting signal in a conventional manner, such as by operation of a push button, the solenoid in the directional control valve 30 is energized by a signal from the main control circuit 70 to change the valve 30 to a position indicated at II, whereby fluid under pressure from the fluid power source, not shown, is accordingly supplied to the right chamber of the cylinder 21 to thereby advance the grinding wheel head 13 at a rapid feeding speed toward the workpiece 42. The limit switch 32 is deactuated by the movement away therefrom of the dog plate 34 with the advancing grinding wheel head 13, to thereby cause operation of the motor 43 for rotating the workpiece 42 and to actuate the coolant supply source 67 for supplying coolant on the contacting surface area of the workpiece 42 and the grinding wheel 15 from the supply nozzle =66. When the forward end of the shaft 23 engages the stop plate 31, the limit switch 33 is actuated by the dog plate 34, whereupon the advancement of the grinding wheel head 13 is stopped at that point, at the time indicated at I in FIG. 4. In this case, as shown in FIG. 4, the grinding wheel is spaced a predetermined distance Al from the Workpiece 42. Actuation of the limit switch 33 causes the switch 56 to be closed and the electrolyte supply source 61 to be actuated, and further the sizing device 64 to be advanced toward the workpiece 42 for measuring the diameter thereof. Consequently, an electrolytic current is impressed between the workpiece 42 and the electrode shoe 52 from the power source 54, and the electrolytic grinding operation is initiated at the electrolytic grinding speed Ve, which designates the removal amount of the workpiece 42 per unit time, from the time t As above described, as the grinding wheel 13 is spaced from the workpiece '42 by a distance Al, the workpiece 42 is not being ground by the grinding Wheel 15. Moreover, a command signal is provided by the main control circuit 70 for causing the pulse generator 71 to emit pulse signals and a gate opening signal is sent to the gate circuit 82. However, before oxide, graphite or the like are formed on the outer surface of the workpiece 42 and while electrolytic resistance between the electrode shoe 52 and the workpiece 42 is still small enough that a large amount of current is flowing in the power circuit, no signal is generated by the comparator 73. Of course, in this instance, a command signal for a fine grinding operation is not emitted from the main control circuit 70. Accordingly, the inhibit signals for the actuation of the comparator 73 and for the fine grinding operation are derived from the NOT gates 77 and 74, respectively, and then sent to the AND gate 76. Therefore, a pulse signal from the pulse generator 71 is sent to the OR gate 75 through the Flip-Flop gate 78 in which the pulse numbers are divided in half, and the AND gate 76, and continuously to the pulse motor 28 through the gate circuit 81 and the driving circuit 84. Thus, the pulse motor 28 is rotated with a rotational speed proportional to the pulses passing through the gate circuit 81 for advancing the grinding wheel head 13 at a slow feed speed Vm from the time t These pulses are added in the reversible counter 83. The electrolytic grinding speed Ve is set up slightly faster than the slow feeding speed Vm for maintaining electrolytic grinding until the electrolytic current falls below the predetermined value. The relationship set up between the speeds Vm and V2 may be varied by changing the output current of the power source 54 or changing the numbers of pulses being generated by the pulse generator 71.

In the meantime, during the electrolytic grinding operatioin, as infusible oxides are formed on the surface of the workpiece 42, or graphites are precipitated from the workpiece 42, electrolytic resistance between the workpiece 42 and the electrode shoe 52 gradually increases, thereby causing the current in the power source 54 to decrease. Consequently, when the electrolytic current falls below the predetermined value, the electrolytic grinding speed Ve slows to the speed Ve from the time t Thus, from the time t after a little while at t the comparator 73 is actuated, and the signal from the NOT gate 77 ceases. Therefore, the pulse signal from the pulse generator 71 is directly sent to the AND gate 72, and through the OR gate 75 and the gate circuit 81 to the driving circuit 84 for driving the pulse motor 28 proportional to the pulse frequency of the pulse generator 71. In consequence, from the time t the grinding wheel head 13 is advanced at a fast feeding speed Vm which of course is twice as fast as the slow feeding speed Vm Thus, the grinding wheel 15 serves to remove the oxide, graphite and the like on the workpiece 42 by a conventional grinding operation, and the electrolytic grinding operation continues to actually grind the workpiece 42. When the electrolytic resistance between the workpiece 42 and the electrode shoe '52 again decreases, whereupon the electrolytic current in the power circuit is increased, the comparator 73 is again disactuated from the time t Accordingly, the pulse signal from the pulse generator 71 is sent to the AND gate 76 through the =Flip-Flop gate 78 for reducing the pluse frequency by half, and the reduced pulse signal frequency is sent to the pulse motor 28 through the OR gate 75', the gate circuit 81, and the driving circuit 85. Thus, the grinding wheel head 13 is again advanced at the slow feeding speed Vm As above described, the workpiece 42 is ground by means of the electrolytic grinding process and the conventional wheel grinding operation, and when the operation is progressed to the time tn, wherein the dimension of the workpiece 42 is at the desired point, a command signal for the fine grinding operation is sent from the Schmitt circuit 88 to the main control circit 70, thereby opening the switch 56 and stopping the flow from the electrolyte supply source 61, thus signaling the completion of the electrolytic grinding operation. At this time, the command signal for fine grinding operation is sent from the main control circuit 70 to the AND gate 79 and the NOT gate 74, respectively, so that the reduced pulse signal from the Flip-Flop gate 78 is sent to the OR gate 75 through the AND gate 79 and the Flip-Flop 80 in which the pulses are further divided in half, and then sent to the pulse motor 28 through the gate circuit 81 and the driving circuit 84 for advancing the grinding wheel head 13 at a fine grinding speed Vm When, at the time t,, the workpiece 42 is finished to the final dimension, the final sizing signal is sent from the Schmitt circuit 89 to the main control circuit 70. Then, the gate closing signal is sent to the gate circuit 81 from the main control circuit 70, thus stopping the grinding wheel head 13. At the same time or a little while deriving the sizing signal, an opening signal for gate 82, namely a reversing pulse motor 28 signal, is sent to the gate circuit 82, and a deenergizing signal is sent from the main control circuit 70 to the solenoid of the directional control valve 30 for changing the position to I. Accordingly, the grinding wheel head 13 is retracted at the composite speed of the rapid feeding speed by the piston 22 and the speed of the pulse motor 28. Then, upon appropriate retraction of the grinding wheel head, the limit switch 33 is deactuated for retracting the sizing device 64 to its initial position. The pulses applied to the pulse motor 28 are subtracted from the reversible counter 83 during reversing rotation of the pulse motor 28. When the number in the counter 83 reaches zero, a stopping signal is sent from the counter 83 to the main control circuit 70 for indicating that the grinding wheel head 13 has been retracted to its starting position. Furthermore, a command signal for stopping the generation of pulse signals and for closing the gate 82 are sent to the pulse generator 71 and the gate circuit 82, respectively. Thus, the grinding cycle is completed, and the workpiece 42 is ground to a final predetermined size.

As above described, in the electrolytic grinding machine formed according to the present invention, a workpiece is ground initially by means only of an electrolytic grinding process until the electrolytic grinding current, namely the electrolytic grinding speed, falls below a predetermined value, whereupon conventional grinding by a grinding wheel is applied to the workpiece for removing the graphite and oxide precipitated theeron. Thereafter, electrolytic grinding current again increases. Thus, it is expected to increase the electrolytic grinding efiiciency and to minimize the Wear and the damage of the grinding wheel.

While the present invention has been described by means of a specific embodiment, various modifications and variations are possible in light of the teachings of the invention. It should be understood, therefore, that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In an electrolytic grinding machine having a grinding wheel rotatably mounted on a grinding wheel head, and a head stock and a tail stock for rotatably supporting a workpiece in operative relationship therewith, the improvement comprising:

an electrolytic grinding device also in operative relationship with said workpiece;

a feed mechanism for reciprocably moving said grinding wheel head toward and away from said workpiece;

a sizing device for measuring the size of said workpiece;

means for detecting the electrolytic grinding current;

and

a control system connected to said detecting means for controlling the speed of said grinding wheel head feed mechanism responsive to said electrolytic grinding current.

2. An electrolytic grinding machine as set forth in claim 1, wherein said electrolytic grinding device comprises an electrode shoe having a supply port, a workpiece receiving surface, an electrolyte delivery port in said surface, and insulating particles secured on said surface for spacing the workpiece a predetermined distance from said receiving surface, said shoe supply port being connected to a source of electrolyte, and a power source connected to said shoe and said workpiece.

3. An electrolytic grinding machine as set forth in claim 2, wherein said workpiece-receiving surface of electrode shoe is an arcuate convex surface.

4. An electrolytic grinding machine as set forth in claim 2, wherein said electrolytic power source is a direct-current power source.

5. An electrolytic grinding machine as set forth in claim 1, wherein said detectin means comprises a shunt.

6. An electrolytic grinding machine as set forth in claim 1, wherein said feed mechanism comprises:

a rapidly feeding hydraulic actuator mounted on a machine bed and connected to said grinding wheel head for moving said grinding wheel head through a predetermined linear path whereby said grinding wheel is positioned in predetermined spaced relation with respect to said workpiece; and

a fast, slow and fine finish feeding device for said grinding wheel head for further advancing the same toward said workpiece.

7. An electrolytic grinding machine as set forth in claim 6, wherein said fast, slow and fine feeding device comprises a pulse motor actuable by a signal from said control system.

8. An electrolytic grinding machine as set forth in claim 7, wherein said pulse motor is an electro-hydraulic pulse motor.

9. An electrolytic grinding machine as set forth in claim 8, wherein said control system comprises:

a pulse generator for supplying pulse signals to said pulse motor;

a comparator connected to said electrolytic current detecting means;

first, second, and third control gates for controlling said grinding wheel head feeding speed provided between said pulse generator and said pulse motor;

said first control gate for operating said feeding device at said slow speed responsive to a normal electrolytic grinding speed;

said second control gate for controlling said fast feeding speed being responsive to a signal from said comparator upon a predetermined decrease in said electrolytic grinding speed; and

said third control gate for said fine finish feeding speed being responsive to a signal from said sizing device.

TA-HSUNG TUNG, Primary Examiner us. c1. X.R. 

